The influence of ambulance offload time on 30-day risks of death and re-presentation for patients with chest pain

Abstract

Objective: To assess whether ambulance offload time influences the risks of death or ambulance re-attendance within 30 days of initial emergency department (ED) presentations by adults with non-traumatic chest pain.

Design, setting: Population-based observational cohort study of consecutive presentations by adults with non-traumatic chest pain transported by ambulance to Victorian EDs, 1 January 2015 - 30 June 2019.

Participants: Adults (18 years or older) with non-traumatic chest pain, excluding patients with ST elevation myocardial infarction (pre-hospital electrocardiography) and those who were transferred between hospitals or not transported to hospital (eg, cardiac arrest or death prior to transport).

Main outcome measures: Primary outcome: 30-day all-cause mortality (Victorian Death Index data).

Secondary outcome: Transport by ambulance with chest pain to ED within 30 days of initial ED presentation.

Results: We included 213 544 people with chest pain transported by ambulance to EDs (mean age, 62 [SD, 18] years; 109 027 women [51%]). The median offload time increased from 21 (IQR, 15-30) minutes in 2015 to 24 (IQR, 17-37) minutes during the first half of 2019. Three offload time tertiles were defined to include approximately equal patient numbers: tertile 1 (0-17 minutes), tertile 2 (18-28 minutes), and tertile 3 (more than 28 minutes). In multivariable models, 30-day risk of death was greater for patients in tertile 3 than those in tertile 1 (adjusted rates, 1.57% v 1.29%; adjusted risk difference, 0.28 [95% CI, 0.16-0.42] percentage points), as was that of a second ambulance attendance with chest pain (adjusted rates, 9.03% v 8.15%; adjusted risk difference, 0.87 [95% CI, 0.57-1.18] percentage points).

Conclusions: Longer ambulance offload times are associated with greater 30-day risks of death and ambulance re-attendance for people presenting to EDs with chest pain. Improving the speed of ambulance-to-ED transfers is urgently required.

Keywords: Acute coronary syndrome; Emergency services, medical; Public health; Transportation of patients; Treatment outcome.

* We based our model on relationships identified in earlier studies, , , , , , between various factors, ambulance offload delays, and 30‐day clinical outcomes. The acyclic graph facilitates the selection of potentially confounding variables for multivariable models and the identification of collider variables (in this case, none). Causal pathways reported by previous studies are shown in black if relevant to the association of interest (between ambulance offload delay and 30‐day outcomes), and in grey if not. Biasing or confounding pathways and variables are shown as blue arrows and panels, and were included in our adjusted multivariable models.

IQR = interquartile range. * Proportion of 213 544 presentations; graph truncated at 120 minutes because of low numbers by time point (total, 1462 presentations; 0.7% of all presentations).

Restricted cubic splines with a complete case analysis (N = 192 791) for the relationship between offload time and the odds ratio of 30‐day mortality (reference: 15 minutes), adjusted for age, sex, comorbid conditions, clinical observations (except fever), day of the week, season, year, time of presentation (in‐ or out‐of‐hours), and hospital bed number category, and hospital included as a random effect to account for clustering. Adjusted 30‐day mortality at 15 minutes (reference) was 1.31%.